1. Field of the Invention
The invention relates to an optical scanning apparatus. In particular, the invention relates to an optical scanning apparatus, which utilizes a rotary polygonal f-xcex8 lens for deflecting a light beam upon, for example, a scanned object or recording media.
2. Description of the Related Art
FIG. 1 is a drawing for illustrating an optical scanning system of the related art. As shown in FIG. 1, the optical scanning system generally consists of: a semiconductor light source 1, a collimator lens 2, a cylindrical lens 3, a rotary polygonal mirror 4 and an f-xcex8 lens (or toroidal lens) 5. The semiconductor light source 1 emits a light beam, and the light beam is transformed into a collimated light beam by the collimator lens 2. Next, the cylindrical lens 3 adjusts the shape and the focus position of the collimated light beam, and then the light beam impinges upon the rotary polygonal mirror 4. Next, the rotary polygonal mirror 4 with a constant angular velocity deflects the light beam upon the f-xcex8 lens 5, and then the f-xcex8 lens 5 focuses the light beam onto a mirror 6 to form a linear scan. Finally, the mirror 6 reflects the scanning light beam onto the object 7 at linear constant speed. The aspheric surface of an f-xcex8 lens can be designed by referring to U.S. Pat. No. 4,930,850 or U.S. Pat. No. 4,934,772 . . . etc.
In the related art, a rotary polygonal mirror reflects the incoming light beam to generate a scanning light beam, that is to say, a swimming light source. Although the polygonal mirror rotates at a constant angular velocity, the light beam reflected from it impinges on the scanned object at a varied speed. Therefore, the f-xcex8 lens alters the light beam reflected from the rotary polygonal mirror to impinge on the scanned object at a constant speed.
However, if a semiconductor light source is misalignment and emits a light beam with an angle error xcfx86, there will introduce an angle error to 2xcfx86 after the light beam is incident on a rotary polygonal mirror. Moreover, if a rotary polygonal mirror tilts an angle error xcfx86xe2x80x2, it will also introduce an angle error to 2xcfx86xe2x80x2 after the light beam is reflected. Therefore, the rotary polygonal mirror of the related art has the property of increasing angle error, and further decreases the machining accuracy. Furthermore, the scanning light beam, which is reflected by the rotary polygonal mirror, causes a shift amount. Moreover, the defect of the rotary polygonal mirror causes increases the manufacturing time because aligning of the rotary polygonal mirror and f-xcex8 lens takes longer.
An object of this invention is to provide an optical scanning apparatus, which comprises a semiconductor light source, a collimator lens, a cylindrical lens, and a rotary f-xcex8 lens. The rotary f-xcex8 lens alters the propagating direction of the light beam to scan linearly at a constant speed.
A feature of the invention is the inclusion of an f-xcex8 lens rotating at a constant angular velocity. The rotary f-xcex8 lens refracts the light beam to form a linear scan. Therefore, it doesn""t increase the angle error.
By not using a rotary polygonal mirror in the optical scanning apparatus, the number of optical components is reduced. Thereby, the present invention achieves the advantages of easy assembly, low production cost, and compact structure.